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Factor-based dose calculations: basic dosimetric quantities

In-air output ratio or output factor in air, Sc

d

ref

c

ref

Is the ratio of

primary collision water kerma in free-space K

p

per

monitor unit (MU) between an arbitrary collimator setting c and the

reference collimator setting c

ref

at the same location on the beam’s

central axis:

 

M

;

M ;

ref

ref

p

ref

p

d cK

dcK

cS

c

Also known as:

Mini-phantom output ratio

Collimator scatter factor

Head scatter factor

Sc quantifies fluence variations with collimator settings that can

be used in beam modelling and dose calculations.

Usually d

ref

= 10cm and c

ref

=10cm

E

K

d

spectrum

primary

en

E

p

Report pf AAPM TG106: Accelerator beam data commissioning, Med Phys, 35(9), 2008

AAPM TG 74 report, Med Phys 36 (11), 2009